A ligament is a piece of soft, fibrous tissue that connects one bone to another bone in the skeletal system. Ligaments can often become damaged or injured. When injured, ligaments may tear, rupture or become detached from bone. The loss of a ligament can cause instability, pain and eventual increased wear on the joint surfaces, which can lead to osteoarthritis.
Various surgical techniques have been developed for ligament repair. The surgical technique that is used depends on the ligament that has been damaged and the extent of the injury.
A ligament that is commonly injured is the anterior cruciate ligament (ACL). As seen in FIG. 1, the ACL 5 traverses from the top of the tibia 10 to the bottom of the femur 15.
Trauma to the knee can cause injury to the anterior cruciate ligament (ACL). The ACL may become partially or completely torn. FIG. 2 depicts a diagram representation of a torn ACL 5 in the right knee.
A torn ACL reduces the stability of the knee joint and can result in pain, instability and additional wear on the cartilage surfaces of the knee, resulting in eventual osteoarthritis.
Several surgical techniques and ligament fixation devices are available for ACL repair. One of the most commonly used ACL repair techniques involves removal of the native ACL ligament remnants, drilling tunnels in both the femur and the tibia, inserting a tissue graft into the tunnels in place of the native ACL and securing the tissue graft in place with interference screws or other fixation devices.
Looking now at FIG. 3, after removal of the injured native ACL, currently available aiming instruments are aligned to the tibia and a guide pin is drilled into the tibia. FIG. 3 illustrates a typical aiming device 20 for locating a guide pin (or guide wire) 25 from the outside of the tibia 10 to an exit point inside the joint at the corresponding location of the tibial ACL insertion. Note that the guide pin 25 enters at an angle α to the tibia, and exits into the joint space at the angle α as measured from the upper surface of the tibia (also known as the tibial plateau).
The aiming device 20 is then removed from the tibia 10, leaving the guide wire 25 in place. A special cannulated drill 30 (i.e., a drill with a center hole through the length of the drill) is slid over the guide wire 25 and drilled from the front surface of the tibia 10 into the joint space of the knee. FIG. 4 shows the guide pin 25 and the cannulated drill 30 after drilling through the tibia.
A similar process is followed for drilling into the femur (FIG. 5). The guide pin 25 is inserted through the tibial tunnel 35 into the femur 15 near the femoral insertion site of the native ACL, and then the femoral tunnel 40 is drilled into femur 15, as shown in FIG. 5.
The method described above and shown in FIG. 5 is sometimes referred to as transtibial femoral tunnel drilling since the femoral tunnel 40 is drilled by access through the tibial tunnel 35. One problem with transtibial femoral tunnel drilling is that the femoral tunnel location ends up higher in the femoral notch than the normal anatomic femoral insertion of the ACL because access to the femur is limited by the size and location of the tibial tunnel 35. An alternative method that has been developed and is in current use is to create the femoral tunnel by drilling through the anteromedial portal 45 (FIG. 6). Anteromedial (AM) portal drilling of the femoral tunnel 40 involves drilling across the knee joint through the AM portal skin incision 45 such that the femoral tunnel location can be brought into a more anatomic position. In AM portal drilling, a guide pin 25 is first drilled into the anatomic location on the femur through the AM portal 45, followed by drilling with a cannulated drill 30 as shown in FIG. 6. The guide pin 25 and the cannulated drill 30 enter the AM portal 45 and traverse across the joint space. As shown in FIG. 6, it is clear that the guide pin 25 and drill 30 must pass in front of the adjacent femoral condyle to prevent damaging the condyle. The knee quite often must be put into a state of deep flexion in order to reach the anatomic ACL footprint on the femur and still safely pass by the adjacent condyle and the tibial plateau.
With the tibial tunnel 35 and the femoral tunnel 40 created, the tissue graft 50 (FIG. 7A) is prepared. The tissue graft 50 is typically harvested from the patient's own body tissue and may be hamstring tendons, quadriceps tendon, or patellar tendon. Alternatively, similar tissue grafts may be harvested from a donor and also include the Achilles tendon, anterior tibialis tendon or other graft sources. The graft 50 is first prepared by creating one long tissue graft strand, folding the graft over onto itself, and making measurements along the graft. See FIG. 7A. Example measurements for adults are 30 mm of graft length for the portion of the graft that is inserted into the femoral tunnel, 27 mm of graft length for the portion of the graft that is intra-articular (inside the knee joint) and 35 mm of graft length for the portion of the graft that is inserted inside the tibial tunnel. The tissue graft 50 is folded over into two bundles 60, 65 as shown in FIG. 7A. Sutures are applied at the areas of the graft 50 that will interface with the tunnel fixation to add additional strength. The folded section 55 will interface with the femoral tunnel 40 and the two opposite ends 60, 65 will be in the tibial tunnel 35.
Additional sutures are looped around the folded portion 55 of the graft 50, forming a strand of sutures 70 (or lead sutures) that can be used to pull the graft 50 into place (FIG. 7B). The lead sutures 70 are passed through the tibial tunnel 35 and femoral tunnel 40, with the assistance of a suture passing guide wire (not shown). FIG. 7B shows the folded over graft in position to be pulled through the tibial tunnel 35 and into the femoral tunnel 40. The lead sutures 70 (upper left in FIG. 7B) are grasped with a clamp 75 outside the femur and the graft construct is pulled through the tibial tunnel 35, through the interior of the knee joint, and into the femoral tunnel 40.
Once the tissue graft 50 is in place, the individual bundles 60, 65 making up the aggregate tissue graft may be manipulated to approximate their anatomic positions.
More particularly, advances in the research of ACL anatomy indicate that there are two primary bundles that make up the natural ACL, the anteromedial bundle 80 (FIG. 8) and the posterolateral bundle 85. The anteromedial bundle 80 and the posterolateral bundle 85 are also sometimes referred to as the AM bundle and the PL bundle. The name of the ligament refers to their point of origin on the tibial plateau, that is, the AM bundle originates anteromedially and the PL bundle originates posterolaterally (relative to each other on the tibial plateau). FIG. 8 illustrates the two bundles and their relative positions in the knee joint. Points A and B (FIG. 8) illustrate the ligament insertions on the tibial plateau as well as the ligament insertions on the femur. The AM and PL bundles cross each other during normal flexion of the knee joint. The AM and PL bundles are roughly parallel to each other when the knee is in full extension.
In the typical surgical technique, the tissue graft 50 is manipulated into positions (FIG. 9) such that the two graft strands 60, 65 (making up the aggregate tissue graft) approximate the locations of the AM and PL bundles and yield a reconstruction that approximates the native ACL anatomy. It has been demonstrated in biomechanical tests that this construct results in a more stable result. There are several techniques and devices which are used to approximate the footprint of the AM and PL bundles.
After the AM and PL bundles are manipulated into position, fixation screws 90 (also known as interference screws) are inserted (e.g., into the femoral tunnel 40 and then into the tibial tunnel 35). First the femoral portion of the graft is fixed into place by inserting an interference screw 90 through the AM portal 45 and into the femoral tunnel 40, as shown in FIG. 9. The interference screw 90 squeezes the ligament graft tightly up against the tunnel wall so as to secure the ligament graft in position within the tunnel. As the interference screw 90 is tightened into place, it creates an interference fit between the tunnel, the graft and the screw.
FIG. 10 shows the femoral fixation in place, with the AM bundle approximating its anatomic position and the PL bundle approximating its anatomic position.
Lastly, an interference screw 90 (FIG. 11) is inserted into the tibial tunnel 35, thereby completing the fixation of the tissue graft. FIG. 11 illustrates the final construct.
The foregoing technique has been used for many years for reconstruction of the ACL. This technique has been very successful, but it does have limitations. More particularly, a closer look at the current technique reveals limitations due to the geometry of the drilled holes and the use of currently available fixation devices.
More particularly, because the drill 30 enters the femoral notch at an angle, the entrance of the femoral tunnel 40 into the femur 15 is elliptical (FIG. 12). Note that this is not due to poorly manufactured drills, or poor surgical technique, etc.—it is simply the normal result of drilling a hole into a surface with the drill set at an angle to the surface. This becomes more evident when viewing the tunnel straight into (i.e., perpendicular to) the bone surface, as shown in FIG. 12.
Similarly, because the drill 30 exits the tibial tunnel 35 and enters the interior of the joint at an angle, the shape of the tibial tunnel 35 is elliptical at the entrance to the joint space (FIG. 13). This phenomenon has been documented in various biomechanical studies.
Typical interference screws 90 fixate the graft ligament 50 along the length of the screw and about the perimeter of the screw. However, the portion of the ligament disposed in the elliptical portion of a bone tunnel (i.e., that portion of the bone tunnel that does not form a complete circular cross-section) is not secured against bone, as shown in FIG. 14.
The fixation screw 90 and the ligament graft 50 are represented in FIG. 15. The AM and PL bundles are essentially free to reside wherever they may land around the perimeter of the interference screw and are not secured in the elliptical portion of the bone tunnel, because that elliptical portion of the bone tunnel does not form a complete circular cross-section.
On the tibial side, a similar geometric condition exists (FIG. 16). Furthermore, the taper of the typical interference screw 90 at its distal end, which is disposed near the joint side mouth of the tibial tunnel 35, adds additional laxity to the ligament fixation, as shown in the tibial cross-section of FIG. 16. This figure shows a standard interference screw 90 secured in the tibial tunnel 35. The AM and PL bundles are shown roughly in their anatomic positions. The area at the distal end of the interference screw 90 shows how the ligament 50 is not securely fixated in the area near the distal tip of the screw (i.e., where the ligament enters the joint space). This type of limited fixation may contribute to problems such as the so-called “windshield wiper effect” (where the graft ligament sweeps across the mouth of the bone tunnel, thereby causing abrasion to the graft ligament and to the mouth of the bone tunnel), and joint laxity (due to incomplete fixation of the ligament into its anatomic position).
As discussed above, there are potential problems with current interference screw fixation, i.e., there is a lack of complete fixation of the ligament graft at the entrance of the tunnel to the joint space. The unsecured ligament in the elliptical opening of the bone tunnel may contribute to the windshield wiper effect, biomechanical instability and tunnel widening. Furthermore, the rotational position of the ligament graft in the tunnel is not controlled, which can result in a biomechanical construct that does not reproduce the native anatomy, i.e., the ligament strands 60, 65 may not be properly disposed in the locations of the native AM and PM bundles.
Thus there is a need for new apparatus and method for reconstructing a ligament which addresses deficiencies in the prior art.